#include<iostream>
using namespace std;
const double N=1e-6;
int main()
{
    double x;
    cin>>x;
    double left=0,right=x,mid;
    
    while(right-left>N)
    {
         mid=(left+right)/2;
        if(mid*mid*mid<=x)left=mid;
        else right=mid;
    }
    printf("%.6lf",mid);
}